Particulate refractory inorganic oxide solids, e.g., alumina, have been employed for many years as catalyst supports, or carriers, in natural or synthetic form. For example, synthesis gas, or syn gas (hydrogen and carbon monoxide), is produced from low molecular weight hydrocarbons, primarily methane, reacted in the presence of steam (steam reforming process) or oxygen (partial oxidation process), or both steam and oxygen, at high temperature within a fluidized bed of catalyst, e.g., nickel on an alpha alumina support. Suitably, particulate refractory inorganic oxide solids, notably alpha alumina solids, can be admixed with the catalyst, or catalysts, of the fluidized bed as heat transfer solids to control the temperature of reaction. Processes utilizing the admixtures of catalysts and heat transfer solids in reacting low molecular weight hydrocarbons in the presence of both steam and oxygen, it has been found, have provided overall improved thermal and economic efficiencies in the production of syn gas.
Certain particulate refractory inorganic oxide solids as heat transfer materials are more resistant than others to melting and agglomeration at the severe high temperature oxidizing and reducing conditions encountered in fluidized bed syn gas generation processes. These particulate refractory inorganic oxides permit substantially isothermal reactor conditions in conducting such reactions, at least so long as they resist melting and agglomeration which leads to reduced fluidization quality, gas bubbles of increased size, and inferior mass transfer. Moreover, the mechanical strength of some particulate solids is greater than others, and in any process the particles must be sufficient to withstand the stress and strain of process operations. An important pathway to loss of material from a fluidized bed relates to particle degradation through mechanical attrition and break up of the particles to produce fines. The amount of mechanical fracturing and attrition of the particles that can be tolerated during the operation is necessarily limited, and inevitably, in any process some of the solids particles will be swept from the bed by the ascending fluidization gas, or gases. Process economics often militates against the use of devices which prevent the escape of any fines from the process, and generally, with the devices that are used, some fines are lost from the reactor. Whereas cyclone separators are widely used, and can be used to return major concentrations of the solids particles to the bed, no cyclone separator, or system of cyclone separators can be operated with one hundred percent efficiency. Hence, a significant amount of the particulate solids may escape from the process. Make up solids must therefore be added to the reactor to compensate for this loss; any loss represents waste, and additional cost for collection and disposal.
Sintering and agglomeration of the fluidized bed solids have been found particularly important pathways for fluidized bed degradation, and loss of catalyst activity in high temperature fluidized bed operations for the production of syn gas. Hot spots, particularly as occurs in the zones of oxygen injection, produces sintering and agglomeration of the particles. The temperatures in these zones far exceed the normally high temperature of reaction outside these zones, often by several hundred Fahrenheit degrees. Surface melting of the particles, for any reason whatever, creates a tendency of the particles to fuse, or stick together to form agglomerates; and agglomeration of the particulate solids promotes defluidization of the bed. Particulate heat transfer solids must also be chemically compatible with the catalyst of the fluidized bed for contamination and poisoning of the catalyst cannot be tolerated. Albeit there are a few which stand out as exceptional in a relative sense, no particulate refractory oxide solid is now known which possesses the combination of properties which would render it a heat transfer solid capable of completely withstanding sintering, agglomeration and attrition to the desired degree at the extreme conditions encountered in commercial fluidized bed syn gas operations, particularly commercial fluidized bed syn gas operations at extreme hydrothermal conditions. Thus, there exists an acute need for further improving and maintaining the fluidization characteristics of the bed, or beds, employed in fluidized bed syn gas (FBSG) processes.